... a time the filters became partly blocked with sludge and, to some extent, living organisms (bacteria), and themedium had had t o be chlorinated a.t intervals. It had been found, however, that with the open 24 DISCUSSION ON POLLUTION OF STREAMS : gravity-filters, chlorination was not necessary provided...

... an appreciable reduction in the biochemical oxygen demand of the liquid. Under natural conditions the numberosf bacteria ina river below a sewageoutfall decrease ra.pidly a t increasing distances from the outfall. The numbers of bacteria in sewage effluents can be reduced by mechanical filtration...

... CONTROL BACTERIA PARASITES SCIENCE PURIFICATION IMPROVEMENT ATMOSPHERIC POLLUTION UK IN THE EIELD OF ENVIRON31ENTAL HEALTH 15 Discussion The Author, int,roducing the Paper, said that he was well aware that he was speaking tothe convertedwhenheemphasized the need for co-operation between...